Process for preparing malonic diesters in a reactor with internal heat exchangers

ABSTRACT

A process for preparing malonic diesters by carbonylation of haloacetic esters and reaction with monohydric alcohols and a base in the presence of a transition metal catalyst, preferably a catalytic cobalt carbonyl complex, using a stirred reactor with one or more internal heat exchangers. The stirred reactor preferably contains a sparging stirrer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a process for preparing malonicdiesters by carbonylation of haloacetic esters, in particular alkylchloroacetates, with carbon monoxide and reaction with monohydricalcohols and bases in the presence of transition metal catalysts using areactor with one or more internal heat exchanger(s).

[0003] 2. Description of the Background

[0004] It is known that malonic diesters represented by formula I:

[0005] where R¹ and R² are each, independently of one another, anunbranched or branched alkyl or alkenyl group, a cycloalkyl group or anaralkyl group having from 1 to 30 carbon atoms, preferably an alkylgroup having from 1 to 6 carbon atoms, can be prepared by carbonylationof haloacetic esters represented by formula II:

[0006] where R¹ is as defined above and Hal is a halogen atom, withcarbon monoxide and reaction with a monohydric alcohol of the formulaR²OH, where R² is as defined above and preferably corresponds to theradical R¹ in formula II, using a base in the presence of a transitionmetal catalyst.

[0007] In the carbonylation of compounds of the formula II and reactionwith monohydric alcohols, considerable heat of reaction is liberated. Onan industrial scale, the reaction is therefore customarily carried outin a loop reactor such as a BUSS reactor (DE-A 25 53 931).

[0008] The yields of compounds of the formula I achieved are usuallyabove 90% of theory, based on the amount of haloacetic ester used, evenwhen the reaction is carried out on an industrial scale. With a view tominimizing the production costs, it is therefore particularly importantto optimize the space-time yields. In principle, these can be improvedby increasing the reaction temperature and increasing the startingmaterial concentrations.

[0009] An increase in the reaction temperature is desirable not onlybecause of the associated increase in the reaction rate, but also, inview of the highly exothermic nature of the reaction, because of thegreater temperature difference between reaction medium and coolingmedium.

[0010] However, an increase in the reaction temperature is subject tolimits for a number of reasons. Thus, reaction temperaturessignificantly above 100° C. are not possible because the catalyst isthen generally no longer stable even in the presence of high carbonmonoxide partial pressures.

[0011] It is also known that the yield of malonic diesters, based on theamount of haloacetic esters reacted, drops with increasing reactiontemperature. Thus, the isolated yields of the particularly importantdimethyl malonate are from 2 to 3 percent lower when the reaction iscarried out at 90° C. instead of at 50-70° C. under otherwise unchangedconditions. Conversely, reaction temperatures significantly below 90° C.are not acceptable on an industrial scale because of the considerableincreases in the reaction times associated therewith (JP 57-183 741).

[0012] An increase in the starting material concentration is likewisesubject to restrictions. Thus, the halides formed during the reactionare generally obtained as solid salts. The bases used are alsofrequently crystalline solids under the reaction conditions (for examplesodium carbonate). The formation of salt leads, particularly togetherwith the water formed during the reaction, at comparatively highstarting material concentrations of, for example, 25% solids in thereaction mixture to this mixture no longer being able to be fullyuniformly mixed when carrying out the reaction in a stirred reactor or aloop reactor or BUSS reactor. It has also been found that an increase inthe content of, for example, alkyl chloroacetate and/or dialkyl malonatein the reaction mixture to over 3.75 mol/l of reaction volume isassociated with a reduction in selectivity in conventional reactors.

[0013] Although it is possible to improve the selectivity of thecarbonylation reaction by means of additives to the reaction mixture (JP54 112 818), this can make the work-up of the reaction products moredifficult. Contamination caused by additives is also a considerabledisadvantage in respect of further utilization of the solvent(s), of thecatalyst or of its downstream products and especially of the saltformed.

[0014] Accordingly, there remains a need for a process for producingmalonic diesters which does not suffer from the drawbacks discussedabove.

SUMMARY OF THE INVENTION

[0015] It is an object of the invention to provide a process forpreparing malonic diesters of the formula I by carbonylation ofhaloacetic esters of the formula II with carbon monoxide and reactionwith monohydric alcohols which does not have the abovementioneddisadvantages, and which provides improved space-time yields atsimultaneously unimpaired or improved product selectivity.

[0016] The present inventors have now found, unexpectedly, that veryhigh space-time yields can be achieved if the carbonylation reaction andreaction with the monohydric alcohol is carried out in a stirred reactorprovided with one or more internal heat exchanger(s).

[0017] Accordingly, the present invention accordingly provides a processfor preparing malonic diesters represented by formula I:

[0018] where R¹ and R² are each, independently of one another, anunbranched or branched alkyl or alkenyl group, a cycloalkyl group or anaralkyl group having from 1 to 30 carbon atoms, by carbonylation ofhaloacetic esters represented by formula II:

[0019] where R¹ is as defined above and Hal is a halogen atom,

[0020] using carbon monoxide, a monohydric alcohol of the formula R²OH,where R² is as defined above, a base and a transition metal catalyst,wherein the reaction is carried out in a stirred reactor with one ormore internal heat exchanger(s).

[0021] Thus, the object of the present invention may be accomplishedwith a process for preparing malonic diesters represented by formula Iby carbonylation:

[0022] wherein

[0023] R¹ and R² are each, independently of one another, an unbranchedor branched alkyl or alkenyl group, a cycloalkyl group or an aralkylgroup having from 1 to 30 carbon atoms, comprising:

[0024] reacting a haloacetic ester represented by formula II:

[0025] wherein

[0026] R¹ is as defined above; and

[0027] Hal is a halogen atom, with carbon monoxide, a monohydric alcoholrepresented by the formula R²OH, wherein R² is as defined above, and abase, in the presence of a transition metal catalyst,

[0028] wherein the reaction is conducted in a stirred reactor having atleast one internal heat exchanger.

[0029] A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription.

DETAILED DESCRIPTION OF THE INVENTION

[0030] Using the process of the present invention, for example, it waspossible to use up to 5.2 mol of methyl chloroacetate per liter ofliquid phase of the reaction mixture in the preparation of theindustrially particularly important dimethyl malonate without mixingproblems occurring. In addition, the yields of isolated target product(assay: >99.7%) achieved in this way were, for example, 92.0% and thuscomparable with those obtained under analogous conditions but in greaterdilution in the BUSS reactor (91.5%) or a stirred reactor (91.3%).

[0031] As described above, R¹ and R² are each, independently of oneanother, an unbranched or branched alkyl or alkenyl group, a cycloalkylgroup or an aralkyl group having from 1 to 30 carbon atoms. This rangefor the number of carbon atoms in R¹ and R² includes all specific valuesand subranges therebetween, such as 2, 3, 4, 5, 8, 10, 12, 14, 16, 18,20, 22, 24, 26 and 28. Preferred are R¹ and R² groups having 1 to 8carbon atoms.

[0032] The components can be combined at ambient temperatures (roomtemperature). The reaction temperatures are from 40 to 100° C.,preferably from 50 to 95° C. However, regardless of the type of reactorused, it has been found to be advantageous in terms of high space-timeyields to approach desirable high reaction temperatures of, for example,90° C. continuously via a defined temperature ramp. It has been found tobe particularly advantageous to heat the reaction mixture initially tothe temperature required for starting the reaction, for example 50° C.,before then increasing the temperature stepwise or preferablycontinuously to, for example, 90° C. If desired, an after reaction phasecan follow at the same temperature level or a lower temperature level.

[0033] To provide for good mixing of the carbon monoxide with thesuspension comprising the remaining components of the reaction mixturein the case of the stirred reactor and the stirred reactor with one ormore internal heat exchanger(s), the use of a sparging stirrer isadvantageous. In this way, satisfactory dispersion of the carbonmonoxide in the reaction mixture can be achieved even on an industrialscale without external pumps or compressors having to be used.

[0034] Surprisingly, it has also been found that deposits of the halideformed during the reaction can be largely avoided if a stirred reactorprovided with sparging stirrer and internal heat exchangers as describedin EP-A-0 633 060 and U.S. Pat. No. 5,478,535, both incorporated hereinby reference, hereinafter also referred to as a “BIAZZI” reactor, isemployed.

[0035] With regard to the excellent mixing of the carbon monoxide withthe other components of the reaction mixture in a loop reactor or “BUSS”reactor, it has also surprisingly been found when using a “BIAZZI”reactor for the carbonylation of the haloacetic esters and reaction withthe monohydric alcohol that the catalyst is subject to a significantlylower decomposition rate at the same carbon monoxide partial pressureand the same temperature. This enables higher reaction temperatures tobe achieved and/or a lower than usual amount of transition metalcatalyst to be used, as a result of which the costs of recirculating thelatter to the process are lower.

[0036] The halogen in the haloacetic ester may be chlorine, bromine oriodine. Preference is given to using chloroacetic esters.

[0037] As transition metal catalysts, transition metal complexes ortransition metal complex salts containing transition metals selectedfrom the group consisting of cobalt, ruthenium, palladium and platinummay be used. Cobalt is preferred as the transition metal. As thecatalytic cobalt carbonyl complex, preference is given to using dicobaltoctacarbonyl and species which can be generated therefrom, for examplealkali metal salts, in particular sodium salts, of hydridocobaltcarbonyl.

[0038] As bases, it is possible to use, in particular, alkali metal andalkaline earth metal hydroxides, carbonates and hydrogen carbonates. Thesodium compounds, in particular sodium carbonate, are preferred.

[0039] It has likewise surprisingly been found that the isolated yieldsof malonic diesters of the formula I and thus the selectivities achievedincrease regardless of the type of reactor used if the reaction mixturecomprises not only the haloacetic ester of the formula II, themonohydric alcohol of the formula R²OH, the carbon monoxide, the baseand the transition metal catalyst but also from 0.1 to 60% by weight,preferably from 5 to 40% by weight, particularly preferably from 10 to30% by weight, in each case based on the total reaction mixture, of anonpolar solvent which is inert under the reaction conditions(cosolvent). These ranges for the amount of nonpolar solvent include allspecific values and subranges therebetween such as 0.2, 1, 2, 15, 25 and50% by weight, based on the total reaction mixture. Toluene has beenfound to be a particularly advantageous cosolvent.

[0040] An increasing addition of toluene initially results in increasingisolated yields of the compounds of the formula I. However, one finallyreaches a point of maximum selectivity above which the isolated yieldsof the compounds of the formula I drop sharply.

[0041] The rheological behavior of the reaction mixture displays similartrends to the isolated yields. While small additions of toluene have, asexpected, a small influence on the rheology of the reaction mixture,additions of >60% of toluene, based on the total reaction mixture, whencarrying out the reaction in a stirred reactor or in a loop reactor or aBUSS reactor lead to formation of the salt of reaction in anincreasingly greasy, difficult-to-handle and difficult-to-mix form.Furthermore, deposits of the salt of reaction which can only be partlyremoved by rinsing with the alcohol or alcohol/cosolvent mixture usedare formed.

[0042] Surprisingly, greater amounts of cosolvent can be present in thereaction mixture without the abovementioned problems occurring when thereaction is carried out in the “BIAZZI” reactor. These higher cosolventcontents are in turn surprisingly accompanied by higher isolated yieldsof the malonic diesters of the formula I and thus higher selectivities.Thus, higher isolated yields of, for example, up to 94.3% of theory ofdimethyl malonate (assay: >99.8%) can be achieved when the carbonylationreactions and reactions with the monohydric alcohol are carried out inthe “BIAZZI” reactor with addition of cosolvent, in particular toluene,despite increased starting material concentrations and the associatedincrease in the space-time yields.

[0043] After the reaction is complete, the catalyst is preferablydecomposed by means of oxygen or an oxygen-containing gas.

[0044] A fundamental advantage of a stirred reactor, whether without orwith one or more internal heat exchangers, compared to a loop reactor or“BUSS” reactor is the opportunity of repressurizing the gas phase in thereactor more rapidly. The amounts of carbon dioxide formed during thereaction which are dissolved in the reaction mixture cause strongfoaming in the case of rapid depressurization, and this leads at smallgas-liquid interracial areas to entrainment of liquid and solidcomponents of the reaction mixture. dimethyl malonate prepared in thisway had a purity determined by gas chromatography of >99.5%.

EXAMPLE 2

[0045] Preparation Of Dimethyl Malonate (COMPARATIVE EXAMPLE—“BUSS”Reactor)

[0046] The procedure of Example 1 was repeated, but the reactor used wasa “BUSS” reactor. Due to the reactor principle, the reaction here had tobe carried out on a larger scale than in Example 1.

[0047] The reaction time, measured from the beginning of carbon monoxideabsorption to the achievement of a methyl chloroacetate conversionof >99.5%, was 150 minutes.

[0048] The yield of dimethyl malonate isolated was 91.5% of theory,based on the amount of methyl chloroacetate used. The dimethyl malonateprepared in this way had a purity determined by gas chromatography of>99.5%.

EXAMPLE 3

[0049] Preparation Of Dimethyl Malonate Using A “BIAZZI” Reactor

[0050] The procedure of Example 1 was repeated, but the reactor used wasa “BIAZZI” reactor. Due to the reactor principle, the reaction had to becarried out on a larger scale than in Example 1.

[0051] The reaction time, measured from the beginning of carbon monoxideabsorption to the achievement of a methyl chloroacetate conversionof >99.7%, was 70 minutes.

[0052] The yield of dimethyl malonate isolated was 93.4% of theory,based on the amount of methyl chloroacetate used. The dimethyl malonateprepared in this way had a purity determined by gas chromatography of>99.8%.

EXAMPLE 4

[0053] Preparation Of Dimethyl Malonate (“BIAZZI” Reactor)

[0054] The procedure of Example 3 was repeated, but the amount of methylchloroacetate used was increased to 4.8 mol per liter of reactionvolume. In addition, a toluene content of the reaction mixture of 17.1%by weight was set.

[0055] The total time for filling and emptying the reactor together withthe actual reaction time, measured from the beginning of carbon monoxideabsorption to the achievement of a isolated was 91.3% of theory, basedon the amount of methyl chloroacetate used. The dimethyl malonateprepared in this way had a purity determined by gas chromatography of>99.5%.

EXAMPLE 2

[0056] Preparation Of Dimethyl Malonate (COMPARATIVE EXAMPLE—“BUSS”Reactor)

[0057] The procedure of Example 1 was repeated, but the reactor used wasa “BUSS” reactor. Due to the reactor principle, the reaction here had tobe carried out on a larger scale than in Example 1.

[0058] The reaction time, measured from the beginning of carbon monoxideabsorption to the achievement of a methyl chloroacetate conversionof >99.5%, was 150 minutes.

[0059] The yield of dimethyl malonate isolated was 91.5% of theory,based on the amount of methyl chloroacetate used. The dimethyl malonateprepared in this way had a purity determined by gas chromatography of>99.5%.

EXAMPLE 3

[0060] Preparation Of Dimethyl Malonate Using A “BIAZZI” Reactor

[0061] The procedure of Example 1 was repeated, but the reactor used wasa “BIAZZI” reactor. Due to the reactor principle, the reaction had to becarried out on a larger scale than in Example 1.

[0062] The reaction time, measured from the beginning of carbon monoxideabsorption to the achievement of a methyl chloroacetate conversionof >99.7%, was 70 minutes.

[0063] The yield of dimethyl malonate isolated was 93.4% of theory,based on the amount of methyl chloroacetate used. The dimethyl malonateprepared in this way had a purity determined by gas chromatography of>99.8%.

EXAMPLE 4

[0064] Preparation Of Dimethyl Malonate (“BIAZZI” Reactor)

[0065] The procedure of Example 3 was repeated, but the amount of methylchloroacetate used was increased to 4.8 mol per liter of reactionvolume. In addition, a toluene content of the reaction mixture of 17.1%by weight was set.

[0066] The total time for filling and emptying the reactor together withthe actual reaction time, measured from the beginning of carbon monoxideabsorption to the achievement of a methyl chloroacetate conversionof >99.8%, was 90 minutes. The reaction product obtained after thereaction was complete contained the salt of reaction in readilydispersible, not at all greasy form. Salt of reaction adhering to thereactor walls could, even after a number of experiments, be completelyremoved without problems by rinsing with a methanol/toluene mixture.

[0067] The yield of dimethyl malonate isolated was 92.0% of theory,based on the amount of methyl chloroacetate used. The dimethyl malonateprepared in this way had a purity determined by gas chromatography of>99.8%.

EXAMPLE 5

[0068] Preparation Of Dimethyl Malonate (Stirred Reactor) (COMPARATIVEEXAMPLE)

[0069] The procedure of Example 4 was repeated, but the reactor used wasa simple stirred reactor.

[0070] The reaction product obtained after the reaction was completecontained the salt of reaction in greasy, difficult-to-handle form. Saltof reaction adhering to the reactor walls could no longer be completelyremoved by rinsing with methanol or a methanol/toluene mixture after anumber of experiments.

[0071] The yield of dimethyl malonate isolated was only 87% of theory,based on the amount of methyl chloroacetate used. The dimethyl malonateprepared in this way had a purity determined by gas chromatography of>99%.

[0072] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

[0073] This application is based on German Patent Application Serial No.100 08 903.8, filed on Feb. 25, 2000, and incorporated herein byreference in its entirety.

1. A process for preparing malonic diesters represented by formula I bycarbonylation:

wherein R¹ and R² are each, independently of one another, an unbranchedor branched alkyl or alkenyl group, a cycloalkyl group or an aralkylgroup having from 1 to 30 carbon atoms, comprising: reacting ahaloacetic ester represented by formula II:

wherein R¹ is as defined above; and Hal is a halogen atom, with carbonmonoxide, a monohydric alcohol represented by the formula R²OH, whereinR² is as defined above, and a base, in the presence of a transitionmetal catalyst, wherein the reaction is conducted in a stirred reactorhaving at least one internal heat exchanger.
 2. The process of claim 1 ,wherein the stirred reactor contains a sparging stirrer.
 3. The processof claim 1 , wherein the reaction temperature is increased from aninitial temperature to a final temperature by a preselected temperatureramp.
 4. The process of claim 1 , wherein the reaction mixture furthercomprises from 0.1 to 60% by weight of a nonpolar solvent which is inertunder the reaction conditions.
 5. The process of claim 4 , wherein thenonpolar solvent is toluene.
 6. The process of claim 1 , wherein thereaction time, as measured from the beginning of carbon monoxideabsorption to the achievement of a haloacetic ester conversionof >99.8%, is not more than 90 minutes.
 7. The process of claim 1 ,wherein the haloacetic ester is a chloroacetic ester.
 8. The process ofclaim 1 , further comprising decomposing the transition metal catalystwith oxygen or an oxygen-containing gas.
 9. The process of claim 1 ,wherein the transition metal of the transition metal catalyst isselected from the group consisting of cobalt, ruthenium, platinum andpalladium.
 10. The process of claim 9 , wherein the transition metal iscobalt.
 11. The process of claim 10 , wherein the transition metalcatalyst is dicobalt octacarbonyl.
 12. The process of claim 1 , whereinthe base is selected from the group consisting of alkali metalhydroxides, alkaline earth metal hydroxides, alkali metal carbonates,alkaline earth metal carbonates, alkali metal hydrogen carbonates, andalkaline earth metal hydrogen carbonates.
 13. The process of claim 1 ,wherein R₁ is methyl.